Process for cracking petroleum hydrocarbons



Aug. 1, 1933. WLM, CROSS 1,920,929

PROCESS FOR CRACKING PETROLEUM HYDROCARBONS Filed May 9. 1929 IN VENT ORh/aizer/Y. 6105.5.

"Patented Aug. 1, 1933 PrsoFHcE PROCESS 'FOR CRACKING PETROLEUHYDROCARBONS v 'Walter M. Cross, Kansas City, assignor to GasolineProducts Company, Inc., New York,

N. Y., a Corporation of Delaware Application Mayl), 1929. Serial No.361,632

2 Claims.

This invention relates to improvements in the vprocess and apparatusfor, cracking petroleum hydrocarbons and refers more particularly to aprocess in which the oil, after being brought 5 rapidly to a crackingtemperature, is maintained throughout the necessary time period to con-,summate the cracking at temperatures substantially at or slightly belowthe cracking temperature, The novelty in the invention lies primari- .1yin the maintaining of the oil in the Zone of reactionat temperatures notto, exceed 100 F. T I

"used, either powdered coal, oil, gas, or a mixbelow the crackingtemperature or at temperatures sufficiently high to prevent theagglutina tion of the chemical; condensation products formed in theioil.

The process also offers an operation by means j ,of which carbontroubles usually accompanying oil crackingfare substantiallyeliminatedbecause the g chemical condensation products formed,

. .whichconsist of small'globular bodies, are held insuspension in theliquid, coursing through the apparatus and thisliquid is traveling atasufficient velocity and with turbulence which maintains any separatedbodies suspension in, the .Zi hydrocarbon menstruumL Fig. 1 isadiagrammatic showing of the apparatus in which the process may becarried on.

Referring to the drawing: at 1 is shown a furnace divided intocompartments 2 and 3 by 3 a bridge wall 4., 2 Upon the sides and ceilingof *the compartment 2 are arranged heating tubes which are subjected tothe heat of the combustion gases produced by burning fuel by meansof aburner 6. In the adjacent compart- 3 ment 3 is a bank of tubes 7 whichare subjected to convection heat of the combustion gases passing overthe bridge wall 4.

It will be noted that the cracking tubes in the chamber 2 are subjectedprimarily to radiant 4 heat energy, while the bank of tubes 7 receivesprincipally convection heat. The tubes 5 arrangedupon the reflectingsurfaces of the compartment'Z and on the ceiling of compartment 3 areconnected inc'series to form a continuous -coil.- These tubes areconnected by atransfer 7 line 8 to the tube bank 7.

Connected to thedischarge end of the tube bank 7, by means of atransfer.line 9, is evaporator 10: interposed in the transfer line 9 is apressure'reduction valve 11. The. evaporator has a liquid draw-off line12 at the bottom, controlled by a valve 13. vaporized overhead material'passes off through the pipe 1; and is'introduced near the bottom of thebubble tower 15.. ,The' bubble tower, or fractionator, has a gas reliefline 24', regulated by a valve 25 and a liquid draw-01f line26,-controlledby a Valve 27.

In the furnace any suitable type of fuel is ing purposes, includingkerosene, gas oil, fuel oil,

or derivatives thereof, is supplied through the pipe 38'and iscirculated through a preheating coil 3%,"positioned in the upper part ofthe hubble tower. The preheated oil is then directed by means-of a pipe35 to the cracking tubes 5,

positioned in the chamber 2. In the cracking tubes, the oil is raisedrapidly to a crackingtemperature so that, on being discharged from thecracking tubes through the'discharge line 8, the

temperature has been raised to 7001000 F.,

depending upon the character of the oil undergoing treatment and thetime allowed for cracking. The relation of the heating surface of theradiant tubes designated as 5 in the drawing to the convection bankdesignated as 7 is approximatelyas 2-1. Also the tubes in the convectionbank are arranged sothat the oil, in tray- 'eling therethrough, passesin adirection con-v currently to the direction of the combustion gases,that is, from the top downwardly.

After passing through the reaction tubes, or convection bank, the oil isdischarged through the pipe 9 into the evaporator. At the valve 11 thepressure is reduced and, vwith this reduction of pressure, there is aseparation of vapors and liquid, due to the contained heat in the oiland 1 the pressure reduction. At a point near the, discharge of theconvection bank is a pipe connection 36 by means of which a coolermedium may be introduced from any convenient extraneous lated, by meansof the pump 39, tothe cracking tubes 5. The heavy liquid uneva'poratedin the container 10 is drawn on through the pipe 12 and divertedto fueloil storage. 7 r

The overhead material fromthe bubble tower" is passed through thecondenser 20 and'collected as distillate and gas in the separator 23where proper separation of the constituents is effected.

The amount of reflux condensate or'recycle stock returned from thebubble tower to the cracking tubes is determined by the amount ofdephlegmation necessary which, in turn, is delpendent'lupon thecharacter of the oil undergoing treatment.

, The temperaturecontemplated in the crackjingtubes ranges ,iljomTOW-1000" F., the maximum' temperature being" attained in the dischargeor transfer line 8 which connects the ratubes'or cracking tubes with theconvection bank or reaction tubes. In the reaction zone, whichconstitutes the convection bank of tubes 7, the temperature isnotpermitted tofall more than 100 below'the maximum temperature in thecracking tubes 5. .This'decrease in "temperature '0: approximately 100has been 'found t'o' be approximately the decrease in temperature whichhas no particular effect upon'the agglutination or combination of themolecular particles .of the condensation product accumulating in the oilduring the cracking reaction. ..'The chemical condensation productsformed during the cracking operation consist of small globularbodies'held in suspension iri'the liquid iffcracking stock as it coursesthroughjthe tubes f the cracking apparatus. "males, at the beginning ofthe cracking, are

These globular relat'ively sparsely scattered through the oil and, "asthe oil-cracking proceeds by longer exposure to the crackingtemperature, they become more and 'more abundant but,'under the hightemperaturesImaintained, do not readily stick together nor have atendency to agglutinate. Since thejtemperature of the oil in which theyfloat or are heldin suspension remains ator slightly below. thetemperature at which these condensation products were formed, theparticles seem to re- 1 main as separate"erititiesjand'have no tendencyTtoag'gluti nate or. stick together. The temperatui e may not, however,be decreased materially more' 'than 100 before there is perceived anim-' (mediate tendency upon the part of the particles to accumulate.

The particles as formed are so small that it is necessaryto see them,witha high powered microscope and,when viewed in this manner, havea'decidedBrownian movement The decrease in temperature necessary tocause the particles to Iagglutinat'e or become sticky and have atendency to adhere to one another differs somewhat with thedifierentoils and somewhat with the temlperatures necessary to crackthe'particular types for oils/ 1f the temperature is reduced from '5slightly below the range, which is approximately 100, these condensationproductsbecome sticky and thelittle globular "bodies composing themgradually adhere to one another until their molecular weightis such thatthey are deposited or settle on to the container in which the oil isbeing held, or through which it is being passed.

In normal cracking operations utilizing heating coils and a separatingor reaction chamber, the reduction in temperature'in the separatingchamberis materially in excess of 100; consequently there is a rapidformation or accumulation of the hydrocarbon condensation products andconsiderable quantities of these condensation productsare deposited.

The condensation products mentioned above are formed and are depositedin the usual cracking operation, and are ordinarily known in thepetroleum industry as carbon; but it is not really atrue carbon, but is'a chemical condensation product which has 'a very high percentage ofcarbon and a low percentage of hydrogen in its molecules and also has arelatively high molecular weight.

In the present process, after the cracking operation and reaction periodhave been completed,

ing of the cracking oil during the reaction or cracking periods. Assuggested, at the end of the reaction'period or time thereis provided ameans of sudden" chilling of'the oil to temperatures in excess of 250and normally 350 or more below the'cracking temperature. The cooling andaccompanying vaporization produce violent agitation andthere is notsufllcient time allowedfor any agglutination of the particles to occurwhile'the actual cooling takes place, thus theglobular particles willnot adhere to each other and become sufliciently heavy-to settle out.While it is not possible to prevent all agglutination or'accumulation ofthe separate particles, it can be prevented to such"- an extent that acracking plant may be operated for ninety days or more,jcomp'ared withthe normal ten day period when this agglutination of the particles isallowed to take placein a relatively "quiescent pool of oil andparticularly when the temperature of the M1 Inasmuch as in many verysuccessful cracking processes, the time required for cleaning theapparatus, including the settling tanks, etc. may occupy as much at10-20% of the total operating time, whereas in this method the cleaningoperation may readily lee-reduced to 1-2% of the total operating time,the present process offers a very great saving,particularly in view ofthe fact that the typeof apparatus used maybe constructed withconsiderable less expenditure than where large separators or reactionchambers are supplied. The pressure maintained upon the cracking andreaction zones rangesfrom 500-1000 pounds per square inchand, undernormal operation the pressure -will be maintained "at from 700-900pounds, 'so'that a substantial portion or the oil passing through thesystem is maintained in the liquid phase.

The addition of acooling medium, such as hydrocarbon, in the reactionzone, near the outlet thereof, is to facilitate and increase therapidity with which cooling of theoil is carried on with a reduction ofpressure. The introduction of .a cool hydrocarbon near the discharge ofthe reaction period reduces the temperature below that point at whichstickiness, in the hydrocarbon particles is produced. The fact thatthese particles can be p more or less rapidly frozen within the oil bodyso that they remain in a very finely dispersed condition with notendency towards agglutination e1im-' inates from the operation carbondifiiculties which are inherent to liquid vapor phase cracking processesin use at thepresent time. a

I claim as my invention: v

1. A process of cracking hydrocarbon oil com-- prising the steps ofpassing oil 'through'a section of a continuous coil in a heating zone,efiecting combustion for said heating zone and subjecting the oil duringsubstantially its entire travel through said section of the continuouscoil to the radiant heat of combustion whereby it is rapidly v broughtto a cracking temperature, then passing the oil through another sectionof the coil in a second heating zone where it is subjected to convectionheat from combustion gases derivedfrom said first heating zonecontrolled to maintain the oil at a cracking temperature lower than thecracking temperature attained by it in said first heating zone, thenpassing the oil through another section of the coil in the secondheating zone where the temperature of the oil is rapidly decreased bythe introduction of a cooling medium into the oil, and removing andvaporizing the oil.

2. A process of. cracking hydrocarbon oil com-- I prising the steps ofpassing oil'through a section of a continuous coil heating zone,eifecting combustion for said heating zone and subjecting the oil duringsubstantially its entire travel through said section of the continuouscoil to the radiant heat of combustion whereby it is rapidly broughtdensation products formed during cracking from agglutinating, thenpassing theoilthrough another section of the coil in the second heatingzone where the temperature of the oil is rapidly decreased by theintroduction of a cooler hydrocarbon oil into the oil and removing andvaporizingv the oil. I

WALTER M. CROSS.

